Human influence on the carbon cycle

The preindustrial carbon cycle in Fig. 6.1 is shown as a steady state system, with inputs balancing outputs for each reservoir. Human activity, particularly since the industrial revolution in the mid-1700s, has had a significant influence on the size of fluxes between some of the carbon reservoirs. Since industrialization there has been an imbalance between uptake and release of C02, as can 

Measurements of atmospheric C02 concentrations suggest that the gas is accumulating in the atmosphere more slowly than the rate at which it is being supplied, 

Despite the increased uptake of C02 by some of the surface reservoirs, the net annual surplus input of C02 to the atmosphere was c.3.4Gt during the 1980s (Siegenthaler Sarmiento 1993 Houghton et al. 1996). As can be seen from Fig. 6.33c, the annual rate of increase of atmospheric C02 varies somewhat. 

In preceding sections we have considered the main greenhouse gases, which have natural as well as anthropogenic sources water vapour, carbon dioxide and 

The size of the various natural sources of other gases is less well understood, making anthropogenic contributions difficult to quantify.Table 6.3 shows estimates of 

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